1. Field of The Invention
The present invention relates generally to an apparatus for driving an engine throttle valve to control its opening angle applicable to an internal combustion engine.
2. Description of The Background Art
Recently, a control for a throttle valve of the internal combustion engine having multiple functions is generalized. The multiple functions are 1) a mere interlocking with an accelerator pedal depressed by an operator; 2) a traction control so as to reduce an opening angle of the throttle valve in order to reduce slips of vehicular tire wheels during a vehicular acceleration; and 3) an automatic cruise control such that a constant vehicular speed is maintained with the accelerator pedal open or not depressed. Simultaneously, a fail safe structure such that an overrun of the engine revolution is suppressed with the opening angle of the throttle valve held at a minimum position during a failure of the engine.
A Japanese Patent Application First Publication No. Showa 64-29633 published on Jan. 31, 1989 exemplifies a previously proposed throttle valve opening angle controlling apparatus in which the traction control is carried out.
In the disclosed Japanese Patent Application First Publication, an accelerator drum is rotated in a direction such that the opening operation of the throttle valve is enabled when the accelerator pedal is depressed. Then, the throttle valve is open which is engaged with the accelerator drum via a lever biased in the open direction of the throttle valve. During the traction control, the throttle valve is driven in a closed direction by means of a motor.
However, since, in the previously proposed throttle valve opening angle controlling apparatus, the motor can be driven only in the closed direction, another driving mechanism for the throttle valve becomes necessary when it is necessary to drive the throttle valve in the closed direction in addition to the open direction as in the case of the automatic cruise speed control.
In addition, in a case where the traction control is carried out, a structure of the throttle opening angle controlling apparatus becomes complex since the motor is used to close the throttle valve against a biasing force in the open direction of the lever. Furthermore, since the throttle valve is directly biased in the open direction, the throttle valve would open if a disengagement thereof from the acclerator pedal system occurs.